A muffler that configures an exhaust system installed in an automobile is conventionally known (see Patent Document 1).
As illustrated in FIG. 8A, this type of muffler 200 is provided with an outer shell 202, an inlet pipe 204 to let exhaust gases from an internal combustion engine flow into the outer shell 202, and an outlet pipe 206 to guide the exhaust gases in the outer shell 202 to the atmosphere. The outlet pipe 206 is a tubular member containing multiple holes 208 (hereinafter referred to as exhaust-gas inlet holes) drilled therein in the circumferential direction, and is arranged such that the exhaust-gas inlet holes 208 are arranged inside the outer shell 202. The outlet pipe 206 has to be arranged inside the outer shell 202 such that at least one of the exhaust-gas inlet holes 208 faces against the bottom surface of the outer shell 202. The exhaust-gas inlet hole 208 that is arranged so as to face towards the bottom surface of the outer shell 202 is hereinafter referred to as a designated inlet hole 210 (see FIG. 9).
Generally, the exhaust gases from the internal combustion engine flow into the outer shell 202 through the inlet pipe 204. The exhaust gases in the outer shell 202 flow into the outlet pipe 206 from an opening arranged at one end of the outlet pipe 206 and the exhaust-gas inlet holes 208, and are discharged to the atmosphere.
Generally, when the exhaust gases flow into the outer shell 202, water condenses from the exhaust gases and water Wt pools on the bottom part of the outer shell 202 in such muffler 200 (see FIG. 8B).
FIG. 8A is a diagram to illustrate an inner structure of a conventional muffler; FIG. 8B is a VIIIB-VIIIB cross-sectional view of FIG. 8A. FIG. 9 is an enlarged view of an outlet pipe illustrated in FIG. 8B
The water Wt pooled inside the outer shell 202 is discharged to the atmosphere when the internal combustion engine rotates at a high rotational frequency, for example, at 700 rpm or higher, and the flow of the exhaust gases inside an outlet pipe 206 is accelerated. More specifically, when the flow of the exhaust gases becomes faster, pressure inside the outer shell 202 becomes negative; thereby the water Wt flows into the outlet pipe 206 and is discharged to the atmosphere through multiple holes drilled in the outlet pipe 206.